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Tuesday, September 08, 2009

The placebo effect is hard wired into the brain

It has been assumed that 'higher' brain structures linked to expectation are involved with sham treatments that can relieve pain, and natural opioid pathways are known to be important players. Now Eippert and colleagues have imaged the brains of volunteers given a sham ointment to relieve a mild burning pain. Half of them had been treated with naloxone, a chemical that blocks opioid signalling. They observed that placebo-related brain activity occurs in both the prefrontal cortex and more hard-wired areas, such as the amygdala, hypothalamus and parts of the brainstem. Here is more detail from their abstract:

Naloxone reduced both behavioral and neural placebo effects as well as placebo-induced responses in pain-modulatory cortical structures, such as the rostral anterior cingulate cortex (rACC). In a brainstem-specific analysis, we observeda similar naloxone modulation of placebo-induced responses in key structures of the descending pain control system, including the hypothalamus, the periaqueductal gray (PAG), and the rostral ventromedial medulla (RVM). Most importantly, naloxone abolished placebo-induced coupling between rACC and PAG, which predicted both neural and behavioral placebo effects as well as activation of the RVM. These findings show that opioidergic signaling in pain-modulating areas and the projections to downstream effectors of the descending pain control system are crucially important for placebo analgesia.

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